Self-locking bolt



United States Patent 193,717 7/1877 Lyon [72] Inventor Wllllam J. Busch Jr. 1,780,675 11/1930 Hewitt 151/31 Warm1nster,Pennsylvan1a 2,407,160 9/1946 Kahn..... 151/31 [21 Appl. No. 791,387 2,414,870 l/l947 Harding... 151/22 [22] Filed Jan. 15,1969 2,637,361 5/1953 Nagel 151/14 [45] Patented Nov. 24,1970 3,145,750 8/1964 Wootton 151/14 [73] Assignee Standard Pressed Steel Co. 3,174,521 3/1965 Harvey 151 14 Jenklntown, PA, 3,212,547 10/1965 McKay et a1 151/14 a corporation of Pennsylvania FOREIGN PATENTS 20,191 5/1905 Austria 151/31 [54] SELF-LOCKING BOLT Primary Examiner-Marion Parsons, Jr.

8 Claims, 3 Drawing Figs. Attorney- Stanley Belsky 52 us. m 151114 [51] Int. Cl. ..Fl6b 39/16,

Flfib 39/30 ABSTRACT: A self-locking bolt in which the thread portion [50] Field of Search 85/ 1F, lSS, f h ho" is permanently distorted to have an oblate external I v 1.5; 151/22, 31, 70 cross section. The bolt is provided with a stepped counterbore extending axially of the bolt from the point of the bolt toward [56] References Cited the head of the bolt. The oblate external cross section extends UNITED STATES PATENTS selected axial lengths in both directions from the step of the 151131 counterbore.

SELF-LOCKING sour The present invention relates, in general, to self-locking joint. For the most'part, all these metal lockbolts have suffered from one or moreshortcomings or.limitations. In certain instances it has beenfoundthat the lockbolt has limited, if any, reusability. In other instances, it has been found that the particular arrangement,'while providing the desired locking characteristic, weakened the bolt in terms of tensile strength; Another shortcoming of previously used allmetal lockbolts has been the detrimental effect the locking characteristic of the bolt has had on thefemale thread into which the bolt has been turned. Often the bolt thread has caused excessive wear of the female thread. r

7 Accordingly, it is an object of the present invention to provide a new and improved lockbolt.

' It is another object of the present invention to provide a lockbolt which is not subject to the limitations and -short-.

comings of previously developed comparable devices.

It is yet another object of the presentinvention to provide a lockbolt which is relatively simple in construction and inexpensive to fabricate.

' These'objects, as well as others, are'achieved in accordance with a preferred embodiment of the present invention by providing a bolt having a threaded portion extending from the point end of the bolt and a recess in the threaded portion extending axially of the'bolt from the point end of the bolt. The axial recess is formed as a first counterbore extending from the point end of the bolt a selected distance into the bolt shank and a second counterbore of smaller cross section than the first counterbore extending from the first counterbore further into the bolt shank; The threaded portion is deformed to impart an oblate external cross section which, extends partially along a selected length of the first counterbore and partially along a selected length of the second counterbore.

For a better understanding of the present invention, together with other and further objects thereof, reference is made'to the following description, taken in connection with the accompanying drawing, and its scope. will be pointed out in the appended claims.

Referring to the drawing:

FIG. I is a perspective view of a lockbolt constructed in accordance with the present-invention;

FIG. 2 is a sectional view taken along 2-2 of FIG. 1; and

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2.

Referring to the drawing, a lockbolt l0, constructed in accordance with the present invention, includes a shank 12 having a threaded portion 14 extending from the point end of the bolt. An enlarged head 16 is provided at the opposite end of the bolt and is integral with shank 12. Although in the embodiment of the invention illustrated, head 16 is shown as having a twelve-point drive configuration, it will be apparent that various other wrenching configurations may be employed.

Extending axially of bolt from the point end is a stepped counterbore. This stepped counterbore includes a first counterbore 20 extending from the point end of the bolt a selected distance into threaded portion l4 and a second counterbore 22, of small cross section than counterbore 20, extending from counterbore 20 further into threaded portion M. Counterbores 20 and 22- are concentric and are centered on the iongitudinal axis of the bolt. The dimensions of counterbores 20 and 22 may vary from one application to another and with the choice of materials used in fabricating the bolt. The inclined shonlder 24 between counterbores 20 and 22 and the conical 'recess 25 at the innermost end of counterbore 22, while resulting from the manner in which the counterbores are drilled or formed in the bolt, reduce the tendency of developing stress concentrations within the bolt as would be developed if these surfaces were perpendicular to the longitudinal axis of boit In.

As most clearly illustrated in FIG. 3, threaded portion 14 has an oblate (elliptical) external cross section. As shown in FIG. 2, the oblate external cross section extends partially along a selected axial length of counterbore 2t and partially along aselected axial length of counterbore 22. The oblate ex temal cross section is achieved by squeezing dies or other suitable apparatus with the center of the squeeze located approximately at the step between counterbores 20 and 22. The result of the elliptical deformation of threaded portion 14 is a deformed length of thread generally designated by reference numeral 26. The transition from undistorted thread at either end of the distorted region to the maximum in the distorted region is gradual. A selected number of undistorted threads are provided at the point end of the bolt to permit starting the bolt into a female thread.

The cross-sectional shapes of counterbores 2t) and 22 are dependent upon when the counterbores are formed in the fabrication of the bolt. If circular holes are drilled prior to squeezing, the counterbores will have an oblate cross section,

'as illustrated in FICL'S. If circular holes are drilled after The deformation'26 of the bolt thread is permanent, yet

only tothe extent that the distorted thread is capable of flexing whenerl'gaging a female thread. As the bolt is turned into a female thread, there is strongfrictional engagement between the bolt threadand the female thread. The resilience of the distorted threaded portion is such that the female thread tends to return the distorted bolt thread to its undistorted condition.

It has been found that a bolt constructed in accordance with the present invention optimizes the locking torque and tensile strength of the bolt and results in limited wear on the female thread into which the bolt is turned. If only a single counterbore of a diameter equal to counterbore 20 were provided, the locking torque would be adequate and since the distorted portion of the thread would be springy, little, if any, wear on the mating female threadwould take place. However, because of the amount of material removed from the point end of the bolt, the tensile strength of the bolt would be lower than desired. On the other hand, if a single counterbore of a diameter equal to counterbore 22 were provided, the tensile strength of the ,bolt and the locking torque are increased. However, the flexibility of the distorted thread portion would be reduced to such an extent that excessive wear on themating female thread would take place.

While there has been described what is, at present consideredto be the preferred embodiment of this invention, it

will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

l. A self-locking male fastener having an externally threaded portion at an end thereof, a f rst counterbore extending from said end a selected distance into said threaded portion, and a second counterbore of smaller cross section than said first counterbore extending from said first counterbore further into said threaded portion, said threaded portion having an oblate external cross section partially along a selected axial length of said first counterbore and partially along a selected axial length of said second counterbore.

2. A self-locking male fastener according to claim 1. wherein said counterbores are concentric and centered on the longitudinal axis of said fastener.

3. A self-locking bolt according to claim 2 wherein said counterbores have oblate cross sections.

from the free end thereof, said threaded shank having an oblate cross section extending selected axial lengths in both directions from the step of said counterbore.

7. A self-locking bolt according to claim 6 wherein said oblate cross section is centered approximately at said step of said counterbore.

8. A self-locking bolt according to claim 7 wherein said stepped counterbore is centered on the longitudinal axis of said threaded shank. 

